The invention set forth in this specification pertains to new and improved adjustable arm structures.
Adjustable arm structures of the type to which this specification pertains are commonly used in offices, drafting rooms and various other related locations to support a lamp of one sort or another in such a manner that the position of the lamp may be easily and conveniently adjusted. They are also commonly used to hold or support document holders such as so called "copy stands" which are often employed to hold a document so that a typist can copy from it. Such arm structures are also on occasion used for a variety of other purposes such as in holding magnifying lens, in holding part trays, in holding various tools and the like.
Although adjustable arm structures used in holding such items have been constructed in a variety of different ways, it is considered that they have normally been constructed so as to each include first and second elongated arm assemblies, a connecting joint for connecting two adjacent ends of the arm assemblies, a mounting joint for use in mounting the entire arm structure on a table, a desk or the like located at the non-connected end of the first arm assembly and a holding joint for holding an item such as a lamp located at the non-connected end of the second arm structure. In such an adjustable arm structure the arm assemblies have usually been constructed so as to each include two parallel links and the ends of these links have been pivotally connected to the various joints indicated.
In such an adjustable arm structure it is conventional to use a spring-normally a coil spring-so that is extends between a link of the first arm assembly and the mounting joint and to use another corresponding spring so that this second spring extends between the connecting joint and a link of the second arm assembly. Such springs will tend to exert forces countering gravity in such a manner that the arm structures are relatively stable in virtually any position to which they can be adjusted. It is also conventional to provide a conventional handle and threaded connections in association with the connecting joint and a link of the second arm assembly to enable the link to be clampled relative to the connecting joint so as to prevent adjustment of the position of the arm assembly.
Adjustable arm structures as indicated in the preceding paragraph are unquestionably highly utilitarian in character. Nevetheless it is believed that there has been a need to improve such structures so that they can be easily and conveniently locked in such a manner that adjustment of the position of the arm assemblies in such structures is effectively precluded. The reason for this need can be readily illustrated with reference to structures as indicated in the preceding. In such structures it is frequently difficult to adequately tighten a handle as noted in order to apply sufficient force to preclude movement when or as a relatively large weight is applied to a holding joint. Such a weight can take the form of a relatively heavy lamp, a heavy book or the like depending upon the use of a specific adjustable arm structure.